Grane is a heavy crude oil field located in the central part of the North Sea. The field is operated by Equinor.
The offshore field was discovered in 1991, and its plan for development and operation (PDO) received approval in 2000. Grane produced first oil in 2003.
Recommended White Papers
Equinor holds a 36.613% stake in the field. The other partners are Petoro (28.905%), Vår Energi (28.3156%) and ConocoPhillips Skandinavia (6.1664%).
Combined total investments were estimated to be NOK15bn ($1.7bn).
Grane Field Location and Geology
Grane oil field is located offshore in the North Sea, around 185km from the Norwegian city of Haugesund. It lies in Block 25/11 at a water depth of around 130m.
The offshore field comprises one main reservoir and some additional segments at a depth of 1,700m. It is estimated that the oil was deposited around 60 million years ago in sandstone from the Tertiary period.
It produces oil with high viscosity primarily from Paleocene sandstone situated in the Heimdal Formation. These sandstones originate from the East Shetland Platform to the West of the field.
With an American Petroleum Institute (API) gravity of 18.5, oil recovered from the field is heavier than most of the crude recovered from the Norwegian sector.
Discovery and Reserves
The field was discovered in 1991 by exploration well 25/11-15. The well was drilled east of the Balder Field complex on the Utsira High to assess the hydrocarbon potential of the Paleocene Heimdal Sand in the Hermod prospect.
It was drilled in November 1991 to a total depth of 2,035m in the Early Jurassic Statfjord Formation.
The well encountered a 64m thick Heimdal Formation Sandstone from 1,734m to 1,798m. The sandstone contained oil down to a clearly defined oil-water contact at 1,787m.
The net pay thickness measured 51.88m, with an average porosity of 34.5% and an average water saturation (Sw) of 12.5%.
Additionally, the well hit the Balder Formation at 1,660m encountering good oil shows, the only oil show recorded outside of the Heimdal Formation.
At the start of production, the Grane field was estimated to contain recoverable reserves of 700 million barrels of oil. However, according to the 2021 plan, recoverable volumes have increased beyond the original PDO estimates to approximately 950 million barrels.
Grane Field Development
The Grane field features an integrated facility for accommodation, drilling, and processing, supported by a steel jacket structure. There are 40 well slots.
Horizontal and multi-lateral wells were drilled to extract oil from the reservoir, while gas was injected to maintain pressure. Initially, 12 pre-drilled wells were linked up to the platform.
In 2010, Grane stopped importing gas from the Heimdal gas centre via a 50km pipeline, and started using produced gas for reinjecting into the reservoir. Gas imports resumed in 2014.
The recovery of oil is maintained through gas injection and drilling of new wells, including sidetracks from existing production wells.
In 2020, Grane was producing at the rate of about 90,000 barrels of oil per day. At peak in March 2006, the field produced 243,000 barrels.
The oil from Grane platform is transported to the Sture terminal in Øygarden west of Bergen via a 212-km pipeline.
At the Sture terminal, the oil is stored in vast rock caverns in the mountainside before shipping it to the global markets.
The Svalin and Breidablikk fields are also tied-back to the Grane platform.
Key Contracts
In May 2000, Kvaerner Oil and Gas received a NOK3.5bn contract to deliver the Grane production module. Under a separate contract, it also built the power generation module and living quarters for the platform.
Safe Service won the contract for flotel rental during the hook-up phase, while Aker Maritime was responsible for the drilling module.
In October 2000, Aker Verdal got a NOK670m contract for the steel jacket for the Grane platform.
Veidekke and Murphy Pipelines secured an engineering, procurement, construction, and installation (EPCI) landpipe contract, while Europipe and Mitsui & Co. Norway provided line pipe for the 217km long export pipeline.
ABB, a multinational electrical engineering corporation, installed the automation system and the electrical system to power the field.
Odfjell Drilling won a drilling contract at the field in April 2001.
In January 2003, Halliburton Energy Services’ Completion Products and Services and Sperry-Sun product service lines were selected by the Grane development partners to offer completion products and services, well intervention services, and multilateral well technology for the field.
Norsk Hydro, which later merged with Equinor (then Statoil), served as engineering, procurement and construction contractor.
